Validation on new row

when I create a new object and add it to the datacontext of my datagrid, it is displayed.
But: if there are any invalid cells, these are not visualized (red border) before I focus in them and foucs out again

I have a observablecollection (of BEModule) = "my business class" as DataContext for the grid
I have error visualization through a red background for invalid data
I add a new object using a new button to this collection( and I do not fill some properties which are required before doing the Add )
The datagrid row appears but the error is shown
When I navigate to a cell that holds an invalid content (empty in this case) and leave it using the mouse , the error visualization appears
But it does not show up when the object is added initially

I have a observablecollection (of BEModule) = "my business class" as DataContext for the grid
I have error visualization through a red background for invalid data
I add a new object using a new button to this collection( and I do not fill some properties which are required before doing the Add )
The datagrid row appears but NOerror is shown
When I navigate to a cell that holds an invalid content (empty in this case) and leave it using the mouse , the error visualization appears
But it does not show up when the object is added initially